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| 型号： | AD876JR |
| 厂商： | Analog Devices Inc |
| 文件页数： | 2/16页 |
| 文件大小： | 0K |
| 描述： | IC ADC 10BIT 20MSPS CMOS 28-SOIC |
| 标准包装： | 27 |
| 位数： | 10 |
| 采样率（每秒）： | 20M |
| 数据接口： | 并联 |
| 转换器数目： | 7 |
| 功率耗散（最大）： | 190mW |
| 电压电源： | 模拟和数字，双 ± |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 28-SOIC W |
| 包装： | 管件 |
| 输入数目和类型： | 1 个单端，单极 |
REV. B
–10–
AD876
+5V
8
6
5
7
1/2
AD826
2
3
6
1/2
AD826
4
REFT
REFB
REFTS
REFTF
REFBS
REFBF
C3
0.1 F
C4
0.1 F
C2
0.1 F
C5
0.1 F
C1
0.1 F
Figure 19. Kelvin Connected Reference Using the AD826
By connecting the op amp feedback through the sense connec-
tions of the AD876, the outputs of the op amps automatically
adjust to compensate for the voltage drops that occur within
the converter. The AD826 has the advantage of being able to
maintain stability while driving unlimited capacitive loads. As a
result, 0.1
F capacitors C1, C2, and C3 can connect directly
to the outputs of the op amps. These decoupling capacitors
reduce high frequency transients. Capacitors C4 and C5 shunt
across the internal resistors of the force sense connections and
prevent instability.
This configuration provides excellent performance and a mini-
mal number of components. The circuit also offers the advan-
tage of operating from a single +5 V supply. While alternative
op amps may also be suitable, consider the stability of these op
amps while driving capacitive loads.
The circuit shown in Figure 20 allows a wider selection of op
amps when compared with the previous configuration. An
AD876
1/2
OP-295
10 F
0.1 F
REFT
REFTS
REFTF
47nF
20k
10
1/2
OP-295
10 F
0.1 F
REFB
REFBS
REFBF
47nF
20k
10
22 F
Figure 20. Kelvin Connected Reference Using the OP295
OP295 dual, single-supply op amp provides stable 3.6 V and
1.6 V reference voltages. The AD822 dual op amp is also suit-
able for single-supply applications. Each half of the OP295 is
compensated to drive the 10
F and 0.1 F decoupling capaci-
tors at the REFTF and REFBF pins and maintain stability.
Like any high resolution converter, the layout and decoupling of
the reference is critical. The actual voltage digitized by the
AD876 is relative to the reference voltages. In Figure 21, for
example, the reference return and the bypass capacitors are
connected to the shield of the incoming analog signal. Distur-
bances in the ground of the analog input, that will be common-
mode to the REFT, REFB, and AIN pins because of the
common ground, are effectively removed by the AD876’s high
common-mode rejection.
High frequency noise sources, VN1 and VN2, are shunted to
ground by decoupling capacitors. Any voltage drops between
the analog input ground and the reference bypassing points will
be treated as input signals by the converter via the reference
inputs. Consequently, the reference decoupling capacitors
should be connected to the same analog ground point used to
define the analog input voltage. (For further suggestions, see
the “Grounding and Layout Rules” section of the data sheet.)
4V
VN1
2V
VN2
REFTF
REFBF
AIN
AD876
Figure 21. Recommended Bypassing for the Reference
Inputs
CLOCK INPUT
The AD876 clock input is buffered internally with an inverter
powered from the DRVDD pin. This feature allows the AD876
to accommodate either +5 V or +3.3 V CMOS logic input sig-
nal swings with the input threshold for the CLK pin nominally
at DRVDD/2.
The AD876’s pipelined architecture operates on both rising and
falling edges of the input clock. To minimize duty cycle varia-
tions the recommended logic family to drive the clock input is
high speed or advanced CMOS (HC/HCT, AC/ACT) logic.
CMOS logic provides both symmetrical voltage threshold levels
and sufficient rise and fall times to support 20 MSPS operation.
The AD876 is designed to support a conversion rate of 20 MSPS;
running the part at slightly faster clock rates may be possible,
although at reduced performance levels. Conversely, some
slight performance improvements might be realized by clocking
the AD876 at slower clock rates.
The power dissipated by the correction logic and output buffers
is largely proportional to the clock frequency; running at reduced
clock rates provides a reduction in power consumption. Figure
8 illustrates this trade-off.
DIGITAL INPUTS AND OUTPUTS
Each of the AD876 digital control inputs, THREE-STATE and
STBY, has an input buffer powered from the DRVDD supply
pins. With DRVDD set to +5 V, all digital inputs readily inter-
face with +5 V CMOS logic. For interfacing with lower voltage
CMOS logic, DRVDD can be set to 3.3 V, effectively lowering
the nominal input threshold of all digital inputs to 3.3 V/2 =
1.65 V.
The format of the digital output is straight binary. Table I shows
the output format for the case where REFTS = 4 V and REFBS
= 2 V.
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| AD876JR-8 | 制造商:Rochester Electronics LLC 功能描述:IC, MONO 8-BIT ADC - Bulk |
| AD876JR-8-REEL | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
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